Is it ALS or PLS?

The short version: There are several motor neuron diseases (“MNDs") diseases that primarily damage the nerves that control your muscles, for reasons that are not yet well-understood. PLS is rarer and less severe than ALS. If you are told you have PLS, it will take years to know if you really have that, or ALS. PLS is not generally considered fatal, though weakened muscles make falls a risk.

The most common reason for being told you have PLS early on is that your legs, where PLS usually begins, are stiff and spastic (twitchy) rather than weak and wasted, and your EMG didn’t show damage to the lower motor neurons as ALS does (though newer, less often available forms of EMG and other specialized tests may confirm upper motor neuron damage). If your disease begins as “PLS,” even if you later progress to “ALS,” you are less likely than other ALS patients to have serious breathing or cognitive impairment.

Definitions of terms:
Primary lateral sclerosis (PLS) is the “only upper motor neuron problems” version of ALS, in which PALS usually have both lower motor neuron (LMN) and upper motor neuron (UMN) damage.

"Upper" motor neurons connect nerves in the spine with nerves in other places, like arms and legs.

"Lower" motor neurons directly control muscles.

So "upper" and "lower" motor neurons have nothing to do with arms vs. legs, for instance.

"Amyotrophic lateral sclerosis" means that the motor neurons that control your muscles die, leading to reduced muscle mass and loss of function.

PLS signs and symptoms
Signs and symptoms of primary lateral sclerosis (PLS) usually take years to progress. They include:

Stiffness, weakness and spasticity in your legs. Legs are the most common site of onset. Sometimes but less often, PLS begins in your tongue or hands and then progresses down your spinal cord to your legs.

Tripping, difficulty with balance and clumsiness

Weakness and stiffness usually progressing to your trunk, then your arms, hands, tongue and jaw

Hoarseness, reduced rate of speaking, slurred speech and drooling caused by weak facial muscles. Like ALS, emotional lability where you veer between laughter and tears (EL) is possible. Unlike with ALS, complete loss of speech is rare.

Difficulties with swallowing and breathing, usually later in the disease

Cognitive impairment can occur but less often and less severely than in ALS.

PLS is differentiated from hereditary spastic paraplegia (HSP) by involving the upper as well as lower limbs, and problems with swallowing/speech rather than epilepsy, deafness, cognitive impairment or eye problems. PLS is also called “progressive symmetric spinobulbar spasticity.”

PLS spares lower motor neurons
In PLS, upper motor neurons are affected, causing stiffness, spasticity and balance issues, but lower motor neurons minimally or not at all. In ALS, both lower and upper motor neurons are involved, though not necessarily equally. That entails more weakness, atrophy and frequently breathing problems than PLS.

In PLS, voluntary muscles are affected, which may include the muscles that control urination, whereas in ALS, involuntary muscles are affected, too. So, in addition to the muscles affected by PLS, ALS often affects the muscles that initiate breathing, and sometimes the muscles that blink and close the eyes, and/or that control bowel movements.

In addition to slower progression than ALS, the symptoms can be worse under certain conditions such as stress, exertion and anger (ALS is fairly constant from hour to hour).

PLS is rarer than ALS
PLS is much rarer than ALS. One study found 5% of MND patients had PLS. The overall prevalence of PLS in the US is estimated only in the hundreds though estimates as high as 2000 have been suggested.

A final PLS diagnosis requires a rear-view mirror
The first clue that someone has PLS rather than ALS is an EMG that does not show many abnormalities, if any, yet someone has stiffness and spasticity without atrophy or weakness. UMN dysfunction is not seen on an EMG, whereas LMN damage is. But suspecting PLS, unlike many other diseases, doesn’t mean the ability to diagnose it.

You may’ve been told you have PLS, but no one can say for sure for several years from when you begin to show symptoms, because lower motor neuron damage can begin years into “PLS.” Features of “PLS” that most often predict “conversion” to ALS if they are present at diagnosis or occur any time thereafter include reduced vital capacity, reduced reflexes, weakness in any single muscle that limits movement, and weight loss.

PLS, like ALS, is a diagnosis of exclusion. One study suggests that if a patient presents with spasticity and does not develop wasting within three years, PLS is very likely. However, since PLS is much rarer than ALS, most patients initially diagnosed with PLS will ultimately be diagnosed with ALS, and the published cutoff for a PLS diagnosis is four years, recognizing that conversion may occur later. Research suggests that the average time from PLS diagnosis to re-diagnosis as ALS is four years, but it can take as long as ten.

Medicare and other benefits
The VA has recognized PLS as a form of ALS, and therefore veterans should apply for service-connected disability benefits. Since PLS is relatively rare, not all claim processors may be familiar, and therefore education will likely be necessary. PLS is not listed separately on the Social Security Administration’s list of impairments but by virtue of the disability it causes, applying for disability should be undertaken when the criteria such as being unable to work are met. The same is true for employers’ disability benefits.

“Converting” to ALS still better than starting with it
A diagnosis that changes from PLS to ALS is a distinct possibility given how rare PLS is. Some experts believe that ultimately all PLS becomes ALS, if you live that long.

However, if you prepare for the worst (ALS) while hoping that your diagnosis stays PLS, you can live your life and adapt to what comes. Wondering every day if you really have ALS can only keep you from living whatever life you have left. Besides, by the time you “convert” and progress, new treatments may be on the horizon.

Research into the clinical features of PLS, UMND ALS and “regular” ALS suggests that localized weakness and/or bulbar onset of symptoms are most predictive of an ultimate ALS diagnosis.

The good news: if you do “convert” from “PLS” to “ALS,” by definition that means that you have “UMND” (upper motor neuron dominant) ALS. And in UMND ALS, survival is longer, cognitive dysfunction is possible (unlike with PLS) but respiratory problems are much less likely than with “regular” ALS.

Research & clinical trials
At this writing, several clinical trials are accepting PLS patients. As with all diseases, do a search on clinicaltrials.gov.

Slower progression, symptomatic treatment
Progression to a wheelchair, if it occurs at all, is generally over years. PLS patients on these Forums most often report beginning to use a power wheelchair after seven years or so, but others have progressed faster.

The average life expectancy of PLS patients has been about 13 years from diagnosis (though recent data suggests it’s longer), but this can be limited by diagnostic confusion, clinics losing track of patients, etc. Still, you can up your odds by eating well, exercising to your capacity, finding the technology to communicate your needs when speech is lost, avoiding falls and addressing breathing issues with BiPAP.

Treatment for PLS, like ALS, focuses on managing symptoms, and assistive devices to compensate for diminished mobility. Because PLS is rarer than ALS, there are no treatments in development for PLS particularly, nor clinics that specialize in it exclusively, but most major MND centers have seen patients who have it. Riluzole may be offered for PLS, though the original trials did not include PLS patients.

The bottom line: If you have to have a motor neuron disease, PLS is the one to have. But if it turns out to be ALS, it’s still a “better” ALS.